The present invention relates to a reflective liquid crystal display device having brightness and high contrast.
A liquid crystal display device is thin and light, therefore, has been widely used as a display for a personal digital assistant. The liquid crystal device does not emit light itself and is a device to express the display by changing the transmissivity and can be driven with several volts of effective voltage. Accordingly, when the liquid crystal display device is used as a reflective one which comprises a reflector provided at the back side of the liquid crystal cell and expresses the display by reflecting the outside light, a display device with an extremely low consumption of electricity can be provided.
A conventional reflective color liquid crystal display device comprises a liquid crystal cell having a color filter and a pair of polarization films by which the liquid crystal cell is sandwiched. In this case, the color filter is provided on one of the substrates of the liquid crystal cell and a transparent electrode is formed on the color filter provided on the substrate. A voltage is applied to the liquid crystal cell to change the alignment of liquid crystal molecule. Accordingly, the transmissivity of each color filter is changed so as to express a color display.
The transmissivity of one polarization film is 45% at most, as a whole. In this case, the transmissivity of the polarization component parallel to the adsorption axis of the polarization film is about 0% and the transmissivity of the polarization component perpendicular to the adsorption axis of the polarization film is about 90%. Accordingly, in a reflective liquid crystal display device comprising two polarization films, when the outside light is incident and reflected by a reflector and goes outside, the light passes through the polarization film four times. As a result, when the transmissivity of the polarization component perpendicular to the adsorption aids of the polarization film is 50% and the light is not adsorbed by the color filter, the reflectance of the outside light is obtained by the following formula.
0.94xc3x9750% =32.8%
Accordingly, when the color filter of the conventional reflective color liquid crystal display device is removed and used as a black and white panel in the same way, the reflectance reaches 33% at most.
In order to brighten the light display, several reflective liquid crystal display devices comprising one polarization film provided on the upper side of a liquid crystal cell that is sandwiched by the polarization film and the reflector have already been proposed. (refer to Japanese Laid-Open Patent Publication No.7-146469 and No.7-84252). In these proposed reflective liquid crystal display devices, the light passes through the polarization film only twice. When the light is not adsorbed by the color filter, the reflectance of the outside light is obtained by the following formula.
0.92xc3x9750%=40.5%
Therefore, these proposed reflective liquid crystal display devices can be expected to increase the reflectance by at most about 23.5% in comparison with that of the liquid crystal display device comprising two polarization films.
A reflective color liquid crystal display device in which color display is expressed by using the birefringence of a twist orientation nematic liquid crystal and polarization film, without using a color filter, has been disclosed in Japanese Laid-Open Patent Publication No.6-308481. A color liquid crystal display device in which birefringence of liquid crystal and phase difference film is used has been disclosed in Japanese Laid-Open Patent Publication No.6-175125 and No.6-301006.
In the reflective liquid crystal display device which expresses color display with color filter and comprises one polarization film to increase the reflectance and to obtain the brightness, however, it is difficult to express a black and white display in achromatic color, especially it is difficult to express a black display in achromatic color with low reflectance. Further, in this reflective liquid crystal display device, the dependency of the reflectance and brightness on the incident direction of the outside light and the observer""s viewing direction, that is, the visual angle dependency of the optical characteristics, is high. When the visual angle dependency of the reflective liquid crystal display device comprising one polarization film is high, the visual angle is narrow and the following problem also occurs. That is, when black brightness is changed greatly with respect to the change of incident direction of the outside light, the optical characteristic of the reflective liquid crystal display device is deteriorated greatly since it is more difficult for the reflective liquid crystal display device to control the incident direction of the outside light in comparison with the transmissive liquid crystal display device.
In the reflective color liquid crystal display in which a color display is expressed by using birefringence of a twist alignment nematic liquid crystal and polarization film, without using a color filter or the color liquid crystal display in which birefringence of liquid crystal and phase difference film is used, since the color filter is not present, the efficient reflectance to obtain the practical brightness can be ensured even if two polarization films are used. However, in the above-mentioned color liquid crystal display devices, since the color display is expressed by using birefringence, it is difficult to express multi-grade and multi-color display such as 16 grade 4096 color display. Further, the range of color purity and color reproduction is also narrow.
In the reflective liquid crystal display device with black and white mode comprising two polarization films, a white display with high reflectance can""t be obtained and the display becomes dark.
In order to solve the above-mentioned problems in the prior art, it is an object of the present invention to provide a reflective liquid crystal display device having low visual angle dependency and preferable optical characteristics, and that can express a black and white display in achromatic color having bright white and a high contrast display.
To accomplish the above-mentioned object, a reflective liquid crystal display device according to a first embodiment of the present invention comprises a polarization film, at least one scattering film, a transparent substrate, a transparent electrode, an alignment layer, a liquid crystal layer, an alignment layer, a metallic reflective electrode and a substrate, which are arranged in that order. According to the first embodiment of the reflective liquid crystal display device, since the scattering film is provided, the collective efficiency of the outside light can be increased to obtain the bright display and in addition, the visual angle dependency can be reduced. Further, since the scattering film is provided dose to the liquid crystal cell an image blur caused by the parallax effect can be prevented.
In the first embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that at least one polymer film is provided between the polarization film and the scattering film. In this case, it is preferable that the polymer film is one selected from a group consisting of polycarbonate, polyalylate and polysulfane.
Further, in the first embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that at least one polymer film is provided between the scattering film and the transparent substrate. In this case, it is preferable that the polymer film is one selected from a group consisting of polycarbonate, polyalylate and polysulfane.
In the first embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the metallic reflective electrode comprises aluminum or silver and is of the specular reflection type. According to this preferable example, the characteristic is not deteriorated by disordering of the alignment of liquid crystal and the visual angle dependency becomes low.
In the first embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the scattering film is a forward scattering film. In this case, it is preferable that a scattering range of the forward scattering film is asymmetric with respect to the normal direction of the film. According to this preferable example, outside light can be collected effectively, and the reflectance characteristic and the contrast characteristic of the front surface become excellent. Further, in this case, it is preferable that a plurality of layered forward scattering films are used and the projection direction of a bisector direction of the angle indicating the scattering range of each forward scattering film to the surface of the film is different. According to this preferable example, natural visual angle characteristics can be obtained at many directions. Further, in this case, it is preferable that two, three or four forward scattering films, which are layered, are used and the projection directions of a bisector direction of the angles indicating the scattering range of each forward scattering film to the surface of the film are at a right angle or anti-parallel to each other.
In the first embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that a color filter layer is provided between the transparent substrate and the transparent electrode.
A reflective liquid crystal display device according to a second embodiment of the present invention comprises a transparent substrate positioned at the upper side, a substrate positioned at the lower side, a liquid crystal cell, two polymer films and a polarization film. A transparent electrode and an alignment layer are provided in that sequential order on the inner side of the transparent electrode positioned at the upper side. A metallic reflective electrode and an alignment layer are provided in that sequential order on the inner side of the substrate positioned at the lower side. The liquid crystal cell, in which nematic liquid crystal as a liquid is filled, is provided between the transparent substrate positioned at the upper side and the substrate positioned at the lower side. Two polymer films are provided outside of the transparent substrate positioned at the upper side of the liquid crystal cell. The polarization film is provided outside of the polymer films. The twist angle of the nematic liquid crystal is selected between 220xc2x0 and 260xc2x0. The product of the birefringence of the nematic liquid crystal xcex94nLC and the thickness of the liquid crystal layer dLC, xcex94nLCxc2x7dLC, is set to be between 0.6 xcexcm and 1.2 xcexcm. One of these polymer films positioned closer to the liquid crystal cell is designated as 1 and the other one is designated as 2. When an extraordinary index of refraction of the inside of each polymer film is designated as nx(i) (i=1,2), an ordinary index of refraction of the inside of each polymer film is designated as ny(i) (i=1,2), and a thickness of each polymer film is designated as dFilm(i) (i=1,2), the retardation of each polymer film, designated as RFilm(i) is obtained by following formula : RFilm(i)=(nx(i)xe2x88x92ny(i))xc2x7dFilm(i) (i=1,2). The birefringence difference, xcex94(R)=(RFilm(1)+RFilm(2))xe2x88x92xcex94nLCxc2x7dLC, which is obtained by using the retardation of the polymer film (RFilm(i)=(nx(i))xe2x88x92ny(i))xc2x7dFilm(i) (i=1,2)) and xcex94nLCxc2x7dLC, is between xe2x88x920.1 xcexcm and xe2x88x920.2 xcexcm. When a reflective liquid crystal display device is seen from the side of the transparent substrate positioned at the upper side, the twist direction of the liquid crystal is designated as the positive direction of rotation, an angle is measured using the horizontal direction as a standard. When the angle of the alignment direction of the liquid crystal molecule on the transparent substrate positioned at the upper side is designated as xcfx86LC the angle of the direction of retardation axis (the direction of extraordinary index of refraction) of the polymer film provided on the side of the liquid crystal cell is designated as xcfx86F1, the angle of the direction of retardation axis (the direction of extraordinary index of refraction) of the polymer film provided on the side of the polarization film is designated as xcfx86F2, the angle of the direction of the adsorption axis of the polarization film is designated as xcfx86P, xcfx86F1xe2x88x92xcfx86LC satisfies 90xc2x0xc2x120xc2x0, xcfx86F2xe2x88x92xcfx86F1 satisfies 45xc2x0xc2x120xc2x0 and xcfx86Pxe2x88x92xcfx86F2 satisfies xe2x88x9245xc2x0xc2x120xc2x0. The second embodiment of the reflective liquid crystal display device can express a black display with low reflectance in achromatic color and a white display with high reflectance in achromatic color, that is, a high contrast display. In addition, since the twist angle of the nematic liquid crystal is selected between 220xc2x0 and 260xc2x0, the excellent characteristic can be obtained even if the liquid crystal display device is driven with a duty ratio of less than 1/200. Furthermore, since xcfx86Pxe2x88x92xcfx86F2 satisfies xe2x88x9245xc2x0xc2x120xc2x0, the birefringence can be utilized with almost maximum efficiency and the utilization rate of light can be increased.
In the second embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the twist angle of the nematic liquid crystal is selected between 240xc2x0 and 260xc2x0, and xcex94nLCxc2x7dLC is determined to be between 0.8 xcexcm and 1.1 xcexcm. According to this preferable example, the excellent characteristic can be obtained even if the liquid crystal display device is driven with a duty ratio of less than 1/240.
In the second embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that RFilm(1) is 0.3 xcexcmxc2x10.1 xcexcm and RFilm(2) is 0.5 xcexcmxc2x10.1 xcexcm. According to this preferable example, the reflectance of black, when an off-voltage is applied, can be decreased.
In the second embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the polymer film is one selected from a group consisting of polycarbonate, polyalylate and polysulfane.
In the second embodiment of the reflective liquid crystal display device, when one of two polymer films positioned closer to the liquid crystal cell is designated as 1 and the other one is designated as 2, an extraordinary index of refraction of the inside of each polymer film is designated as nx(i) (i=1,2), an ordinary index of refraction of the inside of each polymer film is designated as ny(i) (i=1,2), and an index of refraction of the perpendicular direction to each polymer film is designated as nz(i) (i=1,2), the Z coefficient, Qz is obtained by following formula.
Qz(i)=(nx(i)xe2x88x92nz(i))/(nx(i)xe2x88x92ny(i))
In the above formula, it is preferable that Qz(2) is between 0.0 and 1.0. According to this preferable example, the reflective liquid crystal display device having low visual angle dependency can be obtained. In this case, it is preferable that Qz(2) is between 0.3 and 0.7. Furthermore, in this case, it is preferable that Qz(1) is between 0.3 and 0.7.
In the second embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the metallic reflective electrode comprises aluminum or silver and is of the specular reflection type.
In the second embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that at least one scattering film is provided between a polymer film and a liquid crystal cell. In this case, it is preferable that the scattering film is a forward scattering film. In this case, it is preferable that a scattering range of the forward scattering film is asymmetric with respect to the normal direction of the film. Further, in this case, it is preferable that a plurality of layered forward scattering films are used and a projection direction of a bisector direction of the angle indicating the scattering range of each forward scattering film to the surface of the film is different. Further, in this case, it is preferable that two, three or four forward scattering films, which are layered, are used and the projection directions of a bisector direction of the angles indicating the scattering range of each forward scattering film to the surface of the film are at a right angle or anti-parallel to each other.
In the second embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that at least one scattering film is provided between a polarization film and a polymer film. In this case, it is preferable that the scattering film is a forward scattering film. In this case, it is preferable that a scattering range of the forward scattering film is asymmetric with respect to the normal direction of the film. Further, in this case, it is preferable that a plurality of layered forward scattering films are used and a projection direction of a bisector direction of the angle indicating the scattering range of each forward scattering film to the surface of the film is different. Further, in this case, it is preferable that two, three or four forward scattering films, which are layered, are used and the projection directions of a bisector direction of the angles indicating the scattering range of each forward scattering film to the surface of the film are at a right angle or anti-parallel to each other.
In the second embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the metallic reflective electrode is a diffusion reflective type or one having a scattering film which is layered on a specular metallic reflective electrode. According to this preferable example, the reflective liquid crystal display device having a natural change of visual angle characteristic can be obtained.
In the second embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that a transparent substrate is used as a substrate positioned at the lower side, a transparent electrode is provided on the substrate positioned at the lower side instead of metallic reflective electrode and a diffusion reflector comprising aluminum or silver is provided on the outside of the substrate provided at the lower side. According to this preferable example, the reflective liquid crystal display device having a natural change of visual angle characteristic can be obtained. Further, in this case, it is preferable that air is present between the diffusion reflector and the liquid crystal cell.
In the second embodiment of the reflective liquid crystal display device according to the present invention, a color filter layer is provided between a transparent substrate provided at the upper side and a color filter layer.
A reflective liquid crystal display device according to a third embodiment of the present invention comprises a transparent substrate positioned at the upper side, a substrate positioned at the lower side, a liquid crystal cell, two polymer films and a polarization film. A transparent electrode and an alignment layer are provided in that sequential order on the inner side of the transparent electrode positioned at the upper side. A metallic reflective electrode and an alignment layer are provided in that sequential order on the inner side of the substrate positioned at the lower side. The liquid crystal cell, in which nematic liquid crystal as a liquid is filled, is provided between the transparent substrate positioned at the upper side and the substrate positioned at the lower side. Two polymer films are provided outside of the transparent substrate positioned at the upper side of the liquid crystal cell. The polarization film is provided outside of the polymer films. The twist angle of the nematic liquid crystal is selected between 220xc2x0 and 260xc2x0. The product of the birefringence of the nematic liquid crystal xcex94nLC and the thickness of the liquid crystal layer dLC, xcex94nLCxc2x7dLC is set to be between 0.6 xcexcm and 1.2 xcexcm. One of these polymer films positioned closer to the liquid crystal cell is designated as 1 and the other one is designated as 2. When an extraordinary index of refraction of the inside of each polymer film is designated as nx(i) (i=1,2), an ordinary index of refraction of the inside of each polymer film is designated as ny(i) (i=1,2), and a thickness of each polymer film is designated as dFilm(i) (i=1,2), the retardation of each polymer film, designated as RFilm(i) is obtained by the following formula: RFilm(i)=(nx(i)xe2x88x92ny(i))xc2x7dFilm(i) (i=1,2). The birefringence difference, xcex94(R)=(RFilm(1)+RFilm(2))xe2x88x92xcex94nLCxc2x7dLC, which is obtained by using the retardation of the polymer film (RFilm(i)=(nx(i)xe2x88x92ny(i))xc2x7dFilm(i) (i=1,2)) and xcex94nLCxc2x7dLC, is between 0.4 xcexcm and 0.5 xcexcm. When a reflective liquid crystal display device is seen from the side of the transparent substrate positioned at the upper side, the twist direction of the liquid crystal is designated as the positive direction of rotation, and an angle is measured using the horizontal direction as a standard. When the angle of the alignment direction of the liquid crystal molecule on the transparent substrate positioned at the upper side is designated as xcfx86LC, the angle of the direction of retardation axis (the direction of the extraordinary index of refraction) of the polymer film provided on the side of the liquid crystal cell is designated as xcfx86F1, the angle of the direction of the retardation axis (the direction of extraordinary index of refraction) of the polymer film provided on the side of the polarization film is designated as xcfx86F2, the angle of the direction of the adsorption axis of the polarization film is designated as xcfx86P, xcfx86F1xe2x88x92xcfx86LC satisfies 70xc2x0xc2x120xc2x0, xcfx86F2xe2x88x92xcfx86F1 satisfies 60xc2x0xc2x120xc2x0 and xcfx86Pxe2x88x92xcfx86F2 satisfies xe2x88x9220xc2x0xc2x120xc2x0. The third embodiment of the reflective liquid crystal display device can express a black display with low reflectance in achromatic color and a white display with high reflectance in achromatic color, that is, a high contrast display. In addition, since the twist angle of the nematic liquid crystal is selected between 220xc2x0 and 260xc2x0, the excellent characteristic can be obtained even if the liquid crystal display device is driven with a duty ratio of less than 1/200. Furthermore, since xcfx86Pxe2x88x92xcfx86F2 satisfies xe2x88x9220xc2x0xc2x120xc2x0, the birefringence can be utilized with almost maximum efficiency and the utilization rate of light can be increased.
In the third embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the twist angle of the nematic liquid crystal is selected between 240xc2x0 and 260xc2x0, and xcex94nLCxc2x7dLC is determined to be between 0.8 xcexcm and 1.1 xcexcm.
In the third embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that RFilm(1) is 0.75 xcexcmxc2x10.1 xcexcm and RFilm(2) is 0.6 xcexcmxc2x10.1 xcexcm. According to this preferable example, the reflectance of black when an off-voltage is applied can be decreased.
In the third embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the polymer film is one selected from the group consisting of polycarbonate, polyalylate and polysulfane.
In the third embodiment of the reflective liquid crystal display device, when one of two polymer films positioned closer to the liquid crystal cell is designated as 1 and the other one is designated as 2, an extraordinary index of refraction of the inside of each polymer film is designated as nx(i) (i=1,2), an ordinary index of refraction of the inside of each polymer film is designated as ny(i) (i=1,2), and an index of refraction of the perpendicular direction to each polymer film is designated as nz(i) (i=1,2), the Z coefficient Qz is obtained by following formula.
Qz(i)=(nx(i)xe2x88x92nz(i))/(nx(i)xe2x88x92ny(i))
In the above formula, it is preferable that Qz(2) is between 0.0 and 1.0. According to this preferable example, the reflective liquid crystal display device having a low visual angle dependency can be obtained. In this case, it is preferable that Qz(2) is between 0.3 and 0.7. Furthermore, in this case, it is preferable that Qz(1) is between 0.3 and 0.7.
In the third embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the metallic reflective electrode comprises aluminum or silver and is of the specular reflection type.
In the third embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that at least one scattering film is provided between a polymer film and a liquid crystal cell In this case, it is preferable that the scattering film is a forward scattering film. In this case, it is preferable that a scattering range of the forward scattering film is asymmetric with respect to the normal direction of the film. Further, in this case, it is preferable that a plurality of layered forward scattering films are used and the projection directions of a bisector direction of the angles indicating the scattering range of each forward scattering film to the surface of the film is different. Further, in this case, it is preferable that two, three or four forward scattering films, which are layered, are used and the projection directions of a bisector direction of the angles indicating the scattering range of each forward scattering film to the surface of the film are at a right angle or anti-parallel to each other.
In the third embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that at least one scattering film is provided between a polarization film and a polymer film. In this case, it is preferable that the scattering film is a forward scattering film. In this case, it is preferable that a scattering range of the forward scattering film is asymmetric with respect to the normal direction of the film. Further, in this case, it is preferable that a plurality of layered forward scattering films are used and a projection direction of a bisector direction of the angle indicating the scattering range of each forward scattering film to the surface of the film is different. Further, in this case, it is preferable that two, three or four forward scattering films, which are layered, are used and the projection directions of a bisector direction of the angles indicating the scattering range of each forward scattering film to the surface of the film are at a right angle or is anti-parallel to each other.
In the third embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the metallic reflective electrode is a diffusion reflective type or one having a scattering film which is layered on a specular metallic reflective electrode.
In the third embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that a transparent substrate is used as a substrate positioned at the lower side, a transparent electrode is provided on the substrate positioned at the lower side instead of metallic reflective electrode and a diffusion reflector comprising aluminum or silver is provided on the outside of the substrate provided at the lower side. Further, in this case, it is preferable that air is present between the diffusion reflector and the liquid crystal cell.
In the third embodiment of the reflective liquid crystal display device according to the present invention, a color filter layer is provided between a transparent substrate provided at the upper side and a transparent electrode.
A reflective liquid crystal display device according to a fourth embodiment of the present invention comprises a transparent substrate positioned at the upper side, a substrate positioned at the lower side, a liquid crystal cell, two polymer films and a polarization film. A transparent electrode and an alignment layer are provided in that sequential order on the inner side of the transparent electrode positioned at the upper side. A metallic reflective electrode and an alignment layer are provided in that sequential order on the inner side of the substrate positioned at the lower side. The liquid crystal cell, in which nematic liquid crystal as a liquid is filled, is provided between the transparent substrate positioned at the upper side and the substrate positioned at the lower side. Two polymer films are provided outside of the transparent substrate positioned at the upper side of the liquid crystal cell. The polarization film is provided outside of the polymer films. The twist angle of the nematic liquid crystal is selected between 220xc2x0 and 260xc2x0. The product of the birefringence of the nematic liquid crystal xcex94nLC and the thickness of the liquid crystal layer dLC, xcex94nLCxc2x7dLC is determined between 0.6 xcexcm and 1.2 xcexcm. One of these polymer films positioned closer to the liquid crystal cell is designated as 1 and the other one is designated as 2. When an extraordinary index of refraction of the inside of each polymer film is designated as nx(i) (i=1,2), an ordinary index of refraction of the inside of each polymer film is designated as ny(i) (i=1,2), and a thickness of each polymer film is designated as dFilm(i) (i=1,2), the retardation of each polymer film, designated as RFilm(i) is obtained by the following formula: RFilm(i)=(nx(i)xe2x88x92ny(i))xc2x7dFilm(i) (i=1,2). The birefringence difference, xcex94(R)=(RFilm(1)+RFilm(2))xe2x88x92xcex94nLCxc2x7dLC, which is obtained by using the retardation of the polymer film (RFilm(i)=(nx(i)xe2x88x92ny(i))xc2x7dFilm(i) (i=1,2)) and xcex94nLCxc2x7dLC, is between 0.15 xcexcm and 0.3 xcexcm. When a reflective liquid crystal display device is seen from the side of the transparent substrate positioned at the upper side, the twist direction of the liquid crystal is designated as the positive direction of rotation, an angle is measured using the horizontal direction as a standard. When the angle of the alignment direction of the liquid crystal molecule on the transparent substrate positioned at the upper side is designated as xcfx86LC, the angle of the direction of retardation axis (the direction of extraordinary index of refraction) of the polymer film which is provided on the side of the liquid crystal cell is designated as xcfx86F1, the angle of the direction of retardation axis (the direction of extraordinary index of refraction) of the polymer film which is provided on the side of the polarization film is designated as xcfx86F2, the angle of the direction of the adsorption axis of the polarization film is designated as xcfx86P, xcfx86F1xe2x88x92xcfx86LC satisfies 145xc2x0xc2x120xc2x0, xcfx86F2xe2x88x92xcfx86F1 satisfies xe2x88x92120xc2x0xc2x120xc2x0 and xcfx86Pxe2x88x92xcfx86F2 satisfies xc2x145xc2x0xc2x120xc2x0. The fourth embodiment of the reflective liquid crystal display device can express a black display with low reflectance in achromatic color and a white display with high reflectance in achromatic color, that is, a high contrast display. In addition, since the twist angle of the nematic liquid crystal is selected between 220xc2x0 and 260xc2x0, the excellent characteristic can be obtained even if the liquid crystal display device is driven with a duty ratio of less than 1/200. Furthermore, since xcfx86Pxe2x88x92xcfx86F2 satisfies xc2x145xc2x0xc2x120xc2x0, the birefringence can be utilized with almost maximum efficiency and the utilization rate of light can be increased.
In the fourth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the twist angle of the nematic liquid crystal is selected between 240xc2x0 and 260xc2x0, and xcex94nLCxc2x7dLC is determined to be between 0.8 xcexcm and 1.1 xcexcm.
In the fourth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that RFilm(1) is 0.3 xcexcmxc2x110.1 xcexcm and RFilm(2) is 0.75 xcexcmxc2x10.1 xcexcm. According to this preferable example, the reflectance of black when an off-voltage is applied can be decreased.
In the fourth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the polymer film is one selected from a group consisting of polycarbonate, polyalylate and polysulfane.
In the fourth embodiment of the reflective liquid crystal display device, when one of two polymer films positioned closer to the liquid crystal cell is designated as 1 and the other one is designated as 2, an extraordinary index of refraction of the inside of each polymer film is designated as nx(i) (i=1,2), an ordinary index of refraction of the inside of each polymer film is designated as ny(i) (i=1,2), and an index of refraction of the perpendicular direction to each polymer film is designated as nz(i) (i=1,2), the Z coefficient, Qz is obtained by the following formula.
Qz(i)=(nx(i)xe2x88x92nz(i))/(nx(i)xe2x88x92ny(i))
In the above formula, it is preferable that Qz(2) is between 0.0 and 1.0. According to this preferable example, the reflective liquid crystal display device having a low visual angle dependency can be obtained. In this case, it is preferable that Qz(2) is between 0.3 and 0.7. Furthermore, in this case, it is preferable that Qz(1) is between 0.3 and 0.7.
In the fourth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the metallic reflective electrode comprises aluminum or silver and is of the specular reflection type.
In the fourth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that at least one scattering film is provided between a polymer film and a liquid crystal cell. In this case, it is preferable that the scattering film is a forward scattering film. In this case, it is preferable that a scattering range of the forward scattering film is asymmetric with respect to the normal direction of the film. Further, in this case, it is preferable that a plurality of layered forward scattering films are used and a projection direction of a bisector direction of angle indicating the scattering range of each forward scattering film to the surface of the film is different. Further, in this case, it is preferable that two, three or four forward scattering films, which are layered, are used and a projection direction of a bisector direction of the angle indicating the scattering range of each forward scattering film to the surface of the film are at a right angle or anti-parallel to each other.
In the fourth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that at least one scattering film is provided between a polarization film and a polymer film. In this case, it is preferable that the scattering film is forward scattering film. In this case, it is preferable that a scattering range of the forward scattering film is asymmetric with respect to the normal direction of the film. Further, in this case, it is preferable that a plurality of layered forward scattering films are used and the projection directions of a bisector direction of the angles indicating the scattering range of each forward scattering film to the surface of the film is different. Further, in this case, it is preferable that two, three or four forward scattering films, which are layered, are used and the projection directions of a bisector direction of the angles indicating the scattering range of each forward scattering film to the surface of the film are at a right angle or anti-parallel to each other.
In the fourth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the metallic reflective electrode is a diffusion reflective type or one having a scattering film which is layered on a specular metallic reflective electrode.
In the fourth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that a transparent substrate is used as a substrate positioned at the lower side, a transparent electrode is provided on the substrate positioned at the lower side instead of metallic reflective electrode and a diffusion reflector comprising aluminum or silver is provided on the outside of the substrate provided at the lower side. Further, in this case, it is preferable that air is present between the diffusion reflector and the liquid crystal cell.
In the fourth embodiment of the reflective liquid crystal display device according to the present invention, a color filter layer is provided between a transparent substrate provided at the upper side and a transparent electrode.
A reflective liquid crystal display device according to a fifth embodiment of the present invention comprises a transparent substrate positioned at the upper side, a substrate positioned at the lower side, a liquid crystal cell, two polymer films and a polarization film. A transparent electrode and an alignment layer are provided in that sequential order on the inner side of the transparent electrode positioned at the upper side. A metallic reflective electrode and an alignment layer are provided in that sequential order on the inner side of the substrate positioned at the lower side. The liquid crystal cell, in which nematic liquid crystal as a liquid is filled, is provided between the transparent substrate positioned at the upper side and the substrate positioned at the lower side. Two polymer films are provided outside of the transparent substrate positioned at the upper side of the liquid crystal cell. The polarization film is provided outside of the polymer films. The twist angle of the nematic liquid crystal is selected between 220xc2x0 and 260xc2x0. The product of the birefringence of the nematic liquid crystal xcex94nLC and the thickness of the liquid crystal layer dLC, xcex94nLCxc2x7dLC, is set to be between 0.6 xcexcm and 1.2 xcexcm. One of these polymer films positioned closer to the liquid crystal cell is designated as 1 and the other one is designated as 2. When an extraordinary index of refraction of the inside of each polymer film is designated as nx(i) (i=1,2), an ordinary index of refraction of the inside of each polymer film is designated as ny(i) (i=1,2), and a thickness of each polymer film is designated as dFilm(i) (i=1,2), the retardation of each polymer film, designated as RFilm(i), is obtained by the following formula:
RFilm(i)=(nx(i)xe2x88x92ny(i))xc2x7dFilm(i) (i=1,2)
The birefringence difference, xcex94(R)=(RFilm(1)+RFilm(2))xe2x88x92xcex94nLCxc2x7dLC, which is obtained by using the retardation of the polymer film (RFilm(i)=(nx(i)xe2x88x92ny(i))xc2x7dFilm(i) (i=1,2)) and xcex94nLCxc2x7dLC, is between 0.05 xcexcm and 0.15 xcexcm. When a reflective liquid crystal display device is seen from the side of the transparent substrate positioned at the upper side, the twist direction of the liquid crystal is designated as the positive direction of rotation, and an angle is measured using the horizontal direction as a standard. When the angle of the alignment direction of the liquid crystal molecule on the transparent substrate positioned at the upper side is designated as xcfx86LC, the angle of the direction of retardation axis (the direction of extraordinary index of refraction) of the polymer film which is provided on the side of the liquid crystal cell is designated as xcfx86F1, the angle of the direction of retardation axis (the direction of extraordinary index of refraction) of the polymer film which is provided on the side of the polarization film is designated as xcfx86F2, the angle of the direction of the adsorption axis of the polarization film is designated as xcfx86P, xcfx86F1xe2x88x92xcfx86LC satisfies 90xc2x0xc2x120xc2x0, xcfx86F2xe2x88x92xcfx86F1 satisfies xe2x88x9245xc2x0xc2x120xc2x0 and xcfx86Pxe2x88x92xcfx86F2 satisfies xc2x160xc2x0xc2x120xc2x0. The fifth embodiment of the reflective liquid crystal display device can express a black display with low reflectance in achromatic color and a white display with high reflectance in achromatic color, that is, a high contrast display. In addition, since the twist angle of the nematic liquid crystal is selected between 220xc2x0 and 260xc2x0, the excellent characteristic can be obtained even if the liquid crystal display device is driven with a duty ratio of less than 1/200. Furthermore, since xcfx86Pxe2x88x92xcfx86F2 satisfies xc2x160xc2x0xc2x120xc2x0, the birefringence can be utilized with almost maximum efficiency and utilization rate of light can be increased.
In the fifth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the twist angle of the nematic liquid crystal is selected between 240xc2x0 and 260xc2x0 and xcex94nLCxc2x7dLC is determined to be between 0.8 xcexcm and 1.1 xcexcm.
In the fifth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that RFilm(1) is 0.6 xcexcmxc2x10.1 xcexcm and RFilm(2) is 0.5 xcexcmxc2x10.1 xcexcm. According to this preferable example, the reflectance of black when an off-voltage is applied can be decreased.
In the fifth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the polymer film is one selected from a group consisting of polycarbenate, polyalylate and polysulfane.
In the fifth embodiment of the reflective liquid crystal display device, when one of two polymer films positioned closer to the liquid crystal cell is designated as 1 and the other one is designated as 2, an extraordinary index of refraction of the inside of each polymer film is designated as nx(i) (i=1,2), an ordinary index of refraction of the inside of each polymer film is designated as ny(i) (i=1,2), and an index of refraction of the perpendicular direction to each polymer film is designated as nz(i) (i=1,2), the Z coefficient, Qz is obtained by the following formula.
Qz(i)=(nx(i)xe2x88x92nz(i))/(nx(i)xe2x88x92ny(i))
In the above formula, it is preferable that Qz(2) is between 0.0 and 1.0. According to this preferable example, the reflective liquid crystal display device having low visual angle dependency can be obtained. In this case, it is preferable that Qz(2) is between 0.3 and 0.7. Furthermore, in this case, it is preferable that Qz(1) is between 0.3 and 0.7.
In the fifth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the metallic reflective electrode comprises aluminum or silver and is of the specular reflection type.
In the fifth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that at least one scattering film is provided between a polymer film and a liquid crystal cell. In this case, it is preferable that the scattering film is a forward scattering film. In this case, it is preferable that a scattering range of the forward scattering film is asymmetric with respect to the normal direction of the film. Further, in this case, it is preferable that a plurality of layered forward scattering films are used and a projection direction of a bisector direction of the angle indicating the scattering range of each forward scattering film to the surface of the film is different. Further, in this case, it is preferable that two, three or four forward scattering films, which are layered, are used and the projection directions of a bisector direction of the angles indicating the scattering range of each forward scattering film to the surface of the film are at a right angle or is anti-parallel to each other.
In the fifth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that at least one scattering film is provided between a polarization film and a polymer film. In this case, it is preferable that the scattering film is a forward scattering film. In this case, it is preferable that a scattering range of the forward scattering film is asymmetric with respect to the normal direction of the film. Further, in this case, it is preferable that a plurality of layered forward scattering films are used and a projection direction of a bisector direction of the angle indicating the scattering range of each forward scattering film to the surface of the film is different. Further, in this case, it is preferable that two, three or four forward scattering films, which are layered, are used and the projection directions of a bisector direction of the angles indicating the scattering range of each forward scattering film to the surface of the film are at a right angle or is anti-parallel to each other.
In the fifth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the metallic reflective electrode is a diffusion reflective type or one having a scattering film which is layered on a specular metallic reflective electrode.
In the fifth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that a transparent substrate is used as a substrate positioned at the lower side, a transparent electrode is provided on the substrate positioned at the lower side instead of metallic reflective electrode and a diffusion reflector comprising aluminum or silver is provided on the outside of the substrate provided at the lower side. Further, in this case, it is preferable that air is present between the diffusion reflector and the liquid crystal cell.
In the fifth embodiment of the reflective liquid crystal display device according to the present invention, a color filter layer is provided between a transparent substrate provided at the upper side and a transparent electrode.
A reflective liquid crystal display device according to a sixth embodiment of the present invention comprises a transparent substrate positioned at the upper side, a substrate positioned at the lower side, a liquid crystal cell, two polymer films and a polarization film. A transparent electrode and an alignment layer are provided in that sequential order on the inner side of the transparent electrode positioned at the upper side. A metallic reflective electrode and an alignment layer are provided in that sequential order on the inner side of the substrate positioned at the lower side. The liquid crystal cell, in which nematic liquid crystal as a liquid is filled, is provided between the transparent substrate positioned at the upper side and the substrate positioned at the lower side. Two polymer films are provided outside of the transparent substrate positioned at the upper side of the liquid crystal cell. The polarization film is provided outside of the polymer films. The twist angle of the nematic liquid crystal is selected between 220xc2x0 and 260xc2x0. The product of the birefringence of the nematic liquid crystal xcex94nLC and the thickness of the liquid crystal layer dLC, xcex94nLCxc2x7dLC is set to be between 0.6 xcexcm and 1.2 xcexcm. One of these polymer films positioned closer to the liquid crystal cell is designated as 1 and the other one is designated as 2. When an extraordinary index of refraction of the inside of each polymer film is designated as nx(i) (i=1,2), an ordinary index of refraction of the inside of each polymer film is designated as ny(i) (i=1,2), and a thickness of each polymer film is designated as dFilm(i) (i=1,2), the retardation of each polymer film, designated as RFilm(i), is obtained by the following formula: RFilm(i)=(nx(i)xe2x88x92ny(i))xc2x7dFilm(i) (i=1,2). The birefringence difference, xcex94(R)=(RFilm(1)+RFilm(2))xe2x88x92xcex94nLCxc2x7dLC, which is obtained by using the retardation of the polymer film (RFilm(i)=(nx(i)xe2x88x92ny(i))xc2x7dFilm(i) (i=1,2)) and xcex94nLCxc2x7dLC, is between 0.3 xcexcm and 0.4 xcexcm. When a reflective liquid crystal display device is seen from the side of the transparent substrate positioned at the upper side, the twist direction of the liquid crystal is designated as the positive direction of rotation, and an angle is measured using the horizontal direction as a standard. When the angle of the alignment direction of the liquid crystal molecule on the transparent substrate positioned at the upper side is designated as xcfx86LC, the angle of the direction of retardation axis (the direction of extraordinary index of refraction) of the polymer film which is provided on the side of the liquid crystal cell is designated as xcfx86F1 the angle of the direction of retardation axis (the direction of extraordinary index of refraction) of the polymer film which is provided on the side of the polarization film is designated as xcfx86F2, the angle of the direction of the adsorption axis of the polarization film is designated as xcfx86P, xcfx86F1xe2x88x92xcfx86LC satisfies 110xc2x0xc2x120xc2x0, xcfx86F2xe2x88x92xcfx86F1 satisfies xe2x88x9260xc2x0xc2x120xc2x0 and xcfx86Pxe2x88x92F2 satisfies (xc2x145xc2x0xe2x88x9220xc2x0)xc2x120xc2x0. The sixth embodiment of the reflective liquid crystal display device can express a black display with low reflectance in achromatic color and a white display with high reflectance in achromatic color, that is, a high contrast display. In addition, since the twist angle of the nematic liquid crystal is selected between 220xc2x0 and 260xc2x0, the excellent characteristic can be obtained even if the liquid crystal display device is driven with a duty ratio of less than 1/200. Furthermore, since xcfx86Pxe2x88x92xcfx86F2 satisfies (xc2x145xe2x88x9220xc2x0) xc2x120xc2x0 , the birefringence can be utilized with almost maximum efficiency and the utilization rate of light can be increased.
In the sixth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the twist angle of the nematic liquid crystal is selected between 240xc2x0 and 260xc2x0, and xcex94nLCxc2x7dLC is determined between 0.8 xcexcm and 1.1 xcexcm.
In the sixth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that RFilm(1) is 0.5 xcexcmxc2x10.1 xcexcm and RFilm(2) is 0.7 xcexcmxc2x10.1 xcexcm. According to this preferable example, the reflectance of black when an off-voltage is applied can be decreased.
In the sixth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the polymer film is one selected from a group consisting of polycarbonate, polyalylate and polysulfane.
In the sixth embodiment of the reflective liquid crystal display device, when one of two polymer films positioned closer to the liquid crystal cell is designated as 1 and the other one is designated as 2, an extraordinary index of refraction of the inside of each polymer film is designated as nx(i) (i=1,2), an ordinary index of refraction of the inside of each polymer film is designated as ny(i) (i=1,2), and an index of refraction of the perpendicular direction to each polymer film is designated as nz(i) (i=1,2), the Z coefficient, Qz is obtained by the following formula.
Qz(i)=(nx(i)xe2x88x92nz(i))/(nx(i)xe2x88x92ny(i))
In the above formula, it is preferable that Qz(2) is between 0.0 and 1.0. According to this preferable example, the reflective liquid crystal display device having a low visual angle dependency can be obtained. In this case, it is preferable that Qz(2) is between 0.3 and 0.7. Furthermore, in this case, it is preferable that Qz(1) is between 0.3 and 0.7.
In the sixth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the metallic reflective electrode comprises aluminum or silver and is of the specular reflection type.
In the sixth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that at least one scattering film is provided between a polymer film and a liquid crystal cell. In this case, it is preferable that the scattering film is forward scattering film. In this case, it is preferable that a scattering range of the forward scattering film is asymmetric with respect to the normal direction of the film. Further, in this case, it is preferable that a plurality of layered forward scattering films are used and a projection direction of a bisector direction of angle indicating the scattering range of each forward scattering film to the surface of the film is different. Further, in this case, it is preferable that two, three or four forward scattering films, which are layered, are used and the projection directions of a bisector direction of the angle indicating the scattering range of each forward scattering film to the surface of the film are at a right angle or anti-parallel to each other.
In the sixth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that at least one scattering film is provided between a polarization film and a polymer film. In this case, it is preferable that the scattering film is forward scattering film. In this case, it is preferable that a scattering range of the forward scattering film is asymmetric with respect to the normal direction of the film. Further, in this case, it is preferable that a plurality of layered forward scattering films are used and a projection direction of a bisector direction of the angle indicating the scattering range of each forward scattering film to the surface of the film is different. Further, in this case, it is preferable that two, three or four forward scattering films, which are layered, are used and the projection directions of a bisector direction of the angles indicating the scattering range of each forward scattering film to the surface of the film are at a right angle or anti-parallel to each other.
In the sixth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that the metallic reflective electrode is a diffusion reflective type or one having a scattering film which is layered on a specular metallic reflective electrode.
In the sixth embodiment of the reflective liquid crystal display device according to the present invention, it is preferable that a transparent substrate is used as a substrate positioned at the lower side, a transparent electrode is provided on the substrate positioned at the lower side instead of a metallic reflective electrode and a diffusion reflector comprising aluminum or silver is provided on the outside of the substrate provided at the lower side. Further, in this case, it is preferable that an air presents between the diffusion reflector and the liquid crystal cell.
In the sixth embodiment of the reflective liquid crystal display device according to the present invention, a color filter layer is provided between a transparent substrate provided at the upper side and a transparent electrode.